A capsular particle is a particle comprising an outer layer and an inner layer, and has a cavity inside the inner layer and contains a gas, liquid or solid component in the cavity. Capsular particles are being used in various applications, since the particles exhibit characteristic properties as compared to conventional particles. Inter alia, capsular particles comprising a polymer component are anticipated as new high-performance materials.
Specifically, in the case of containing gas in the inner layer, the capsular particles realize whitening under light scattering and weight reduction as a material, and thus there is an on-going development of the material in applications such as pigment for coating material, solvent-based coating material, powdery coating material, weight-reducing resin material, hardware for electronic books, and the like. Furthermore, in the case when liquid or solid is encapsulated in the inner layer, the capsular particles realize the function of releasing the material in the inner layer under certain conditions, and thus there is an on-going development of the material in applications such as toner for dry process photocopiers, repellent for ants, heat storage medium, coating material, adhesive, agrochemical, feedstuff, and immobilized enzyme.
For the polymer which serves as the material for such capsular particles, an amorphous polymer such as polystyrene, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate or the like is used. However, these polymers have low solvent resistance and low heat resistance, and are difficult to handle as fine particles, and thus, their uses have been limited.
In an attempt to solve these problems, U.S. Pat. No. 4,798,691 discloses crosslinked type hollow polymer particles comprising a methyl methacrylate/divinylbenzene copolymer, but there has been a demand for capsular particles comprising a crystalline material having higher solvent resistance and higher heat resistance.
Polyolefin resins represented by polyethylene, polypropylene and the like, which are generally known as crystalline resins having excellent solvent resistance and heat resistance, are expected, due to their properties, to exhibit high performance as capsular particles, but could not be produced by conventional methods for preparing capsular particles. Thus, there has been a demand for capsular fine particles comprising a polyolefin as a novel high-performance material.
Furthermore, capsular fine particles may also be used after molding into a filter, a film or the like, and then functionalizing the surface by methods such as oxidative treatment with strong acid, plasma irradiation, electron beam irradiation, laser irradiation, UV irradiation and the like, and the methods are described in, for example, “Overview of Plastic Coating Technologies” (Industrial Technology Service Center Co., Ltd., p. 251 (1989)).    [Patent Document 1] U.S. Pat. No. 4,798,691    [Non-Patent Document 1] “Overview of Plastic Coating Technologies” (Industrial Technology Service Center Co., Ltd., p. 251 (1989))